Lecture 8 Flashcards
Function of epithelial tissues (5)
Absorption, protection, secretion, excretion, sensory
How does epithelium obtain oxygen and nutrients?
By diffusion from underlying connective tissue, because they are avascular.
3 principal characteristics of epithelium
- cells are closely apposed&adhere to each other (specialized cell to cell junction)
- exhibit functional & molecular polarity (3 surface domains)
- basal surface attached to underlying basement membrane (cell to matrix junction)
what are 3 surface domains?
- free surface/apical domain
- lateral domain
- basal domain
Lateral cell membrane junctions (4)
- Occluding junction (tight junction)
- Anchoring junction (adhering junctions & desmosomes)
- Communicating junction (gap junctions)
- morphologic specialization (lateral cell surface folds ; plecae)
Zonula occludens
Tight junction
Zonula adherens
Adhering junctions
Macula adherens
desmosomes
plicae
Lateral cell surface folds
Functions of zonula occludens
to seal off, separating the luminal space from intercellular space and connective tissue compartment
transmembrane proteins for occluding junctions
claudin, and occludins, ZO-1
Role of occludin
maintains barrier between apical and lateral cell surface
keeps the junction tight
Role of claudin
forms and regulates aqueous channels used for paracellular diffusion (transport of water paracellularly)
What determines permeability through paracellular pathway via occluding junctions?
- number of occluding strands
- Complexity
- Presence of claudins (aqueous channels)
Role of ZO-1
Interact with actin filaments, important link in transduction of signals
Which type of cytoskeleton is present in occluding junction?
actin
What are 2 types of anchoring junctions?
- adhering junctions (zonula adherens)
2. Desmosomes (Macula adherens)
Function of adhering junctions
helps to attach adjacent cells (15-20nm apart, so has intercellular space)
protein for adhering junction
E-cadherin (calcium dependent)
type of cytoskeleton in adhering junction
actin
proteins for desmosomes (macula adherens)
desmoplakins, plakoglobins
desmocolin, desmoglein
what is demosomal attachment plaque made up of?
desmoplakins and plakoglobin
Where is desmocolin and desmoglein attached to?
desmosomal attachment plaque
What is the function of desmosomal attachment plaque?
Interact with intermediate filament
type of cytoskeleton in desmosome
intermediate filament
Purpose of gap junction
to communicate between cells
What is gap junction made up of?
half channel formed by 6 connexin
How is gap junction open?
calcium concentration decrease
What is the purpose of lateral interdigitation?
increase lateral cell surface area to increase fluid volume intercellular space in case it accumulates n the space until driven into underlying connective tissue.
2 Types of basal membrane cell junctions
- Focal adhesion
2. Hemidesmosomes
What is basal lamina composed of (3)?
- Laminin
- Type IV collagen
- Proteoglycan & glycoproteins
Function of basal lamina (5)
- Structural attachment
- Compartmentalization
- Filtration
- Tissue scaffolding
- Regulation and signaling
2 layers of basal lamina
- Lamina lucida
2. Lamina densa
What is under basal lamina?
reticular lamina
What is basement membrane composed of? (3)
Lamina lucida
Lamina densa
Reticular lamina
Purpose of hemidesmosome
helps to anchor epithelial cells(intermediate filaments) to basement membrane
protein for hemidesmosome
integrins
cytoskeleton for hemidesmosome
intermediat filaments
What is hemidesmosome?
cell to extracellular matrix junction
half of desmosome that it only has one attachment plaque
What is a disease Bullous Pemphigoid
Disease characterized by blister formation at epithelium attachment to basement membrane
cytoskeleton for focal adhesion
actin microfilament
Link between actin microfilaments of cytoskeleton and extracellular matrix, playing a role in signal transduction
Focal adhesion
Proteins for focal adhesion (2)
integrin, actin binding proteins
purpose of focal adhesion
anchors the actin microfilament to the extracellular matrix
purpose of basal infoldings
to increase the surface area of the basal domain, allowing for more transport proteins and channels to be present
What types of cells have well-developed basal infolding (2)?
- Kidney tubule
- Striated ducts of exocrine glands
cells that perform active transport of molecules
3 types of exocrine glands
- Merocrine
- Apocrine
- Holocrine
What is merocrine?
exocytosis of membrane-bound vesicles
What is apocrine
Product of released at apical surface surrounded by envelope of cell membrane
ex) mammary gland
What is Holocrine
programmed cell death release secretory product and cell debris (sebaceous glands of skin)
What is endocrine glands?
secrete products into the connective tissue and then entering bloodstream
paracrine signalling?
secreting to nearby cells
autocrine signalling?
secreting to the same cell itself
What is the difference in gland formation between exocrine and endocrine glands?
After proliferation and invagination of cells into connective tissue, duct cells disappear for endocrine glands.
3 shapes of secretory cells
- tubular
- Alvelolar (acinar)
- Tubuloalveolar (tube ends in dilation)
Typical location of simple tubular gland
large intestine
Typical location of simple coiled tubular
Skin sweat gland
Typical location of simple branched tubular
stomach (pylorus) and uterus
Typical location of simple acinar
urethra
Typical location of branched acinar
stomach(cardia) and skin(sebaceous gland)
Typical location of compound tubular
duodenum
Typical location of compound acinar
Pancreas (exocrine portion)
Typical location of compound tubuloacinar
submandibular salivary gland
3 types of secretion
- serous
- mucous
- mixed
characteristics of serous gland (4)
- watery
- oval, rounded nuclei
- apical cytoplasm filled granules stained with eosin
- perinuclear cytoplasm is basophilicdue to rER
Example of serous gland
exocrine pancreas, parotid salivary gland
Chracteristics of mucous gland
- slimy/viscous
- nuclei are flattened and compressed to the edge of cell
- PAS positive (purple color)
- Mucinogen granules (appear empty in H&E staining)
Example of mixed gland
submandibular gland / sublingual gland
Sublingual gland has more serous or mucous?
Mucous
Submandibular gland has more serous or mucous?
serous
What types of secretion does parotid gland secrete?
serous